1. Field of the Invention
This invention is related to lubricating oils and, more particularly, to a class of ashless and nonphosphorus-containing antiwear, antifatigue, and extreme pressure additives derived from cyclic thioureas.
2. Description of Related Art
In developing lubricating oils, there have been many attempts to provide additives that impart antifatigue, antiwear, and extreme pressure properties thereto. Zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as antiwear additives for more than 50 years. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions, and regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, phosphorus, also a component of ZDDP, is suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain undiminished the antiwear properties of the lubricating oil.
In view of the aforementioned shortcomings of the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives that contain neither zinc nor phosphorus.
Illustrative of non-zinc, i.e., ashless, non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazoles and unsaturated mono-, di-, and tri-glycerides disclosed in U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.
U.S. Pat. No. 5,512,190 discloses an additive that provides antiwear properties to a lubricating oil. The additive is the reaction product of 2,5-dimercapto-1,3,4-thiadiazole and a mixture of unsaturated mono-, di-, and triglycerides. Also disclosed is a lubricating oil additive with antiwear properties produced by reacting a mixture of unsaturated mono-, di-, and triglycerides with diethanolamine to provide an intermediate reaction product and reacting the intermediate reaction product with 2,5-dimercapto-1,3,4 thiadiazole.
U.S. Pat. No. 5,514,189 discloses that dialkyl dithiocarbamate-derived organic ethers have been found to be effective antiwear/antioxidant additives for lubricants and fuels.
U.S. Pat. Nos. 5,084,195 and 5,300,243 disclose N-acyl-thiourethane thioureas as antiwear additives specified for lubricants or hydraulic fluids.
U.S. Pat. No. 5,498,809 discloses oil soluble copolymers derived from ethylene and 1-butene that have a number average molecular weight between about 1,500 and 7,500, at least about 30 percent of all polymer chains terminated with ethylvinylidene groups, and an ethylene-derived content of not greater than about 50 weight percent, and which form solutions in mineral oil free of polymer aggregates, as determined by light scattering measurements. Lubricating oil additives, particularly dispersants, produced by the functionalization and derivatization of the these copolymers are said to have enhanced performance (e.g., improved dispersancy and pour point) in lubricating oil compositions, attributable in part to the combination of properties characterizing the copolymers.
The disclosures of the foregoing references are incorporated herein by reference in their entirety.